A racecourse bookmaker is to appear before the British Horseracing Authority on Thursday, charged with having breached the sport's rules on corruption. Matthew Thompson, who has taken bets on-course for 15 years, is said to have laid horses from the stables of Mick Easterby and Bill Moore at a time when he was riding work for those trainers.

Thompson is expected to deny the charges, which relate to 34 races, though his line of defence is unknown. He will represent himself at the hearing, when he will also face a charge of failing to provide complete telephone records on request. If found in breach, he risks being banned from all tracks and licensed premises, killing off his livelihood.

Representatives of both stables confirmed that Thompson had ridden out for them but had not been paid. "Serena Brotherton [an amateur jockey] asked if she could bring him along to teach him how to ride a bit better, so he could take part in a charity race, which was one of the things he wanted to do in life," said David Easterby, assistant trainer to his father, Mick.

"After he'd stopped riding out for us, the secretary automatically put him on the list [of registered stable employees] for the next year without being asked to do so, to make sure that we would be covered from an insurance point of view. And during that period, he's laid our horses and now he's in front of a disciplinary panel because of it."

According to the BHA's records, Thompson was registered at Easterby's yard from 2 October 2007 to June 2008 and at Moore's from 21 February 2008 to December of that year. Moore did not dispute the period when asked about it.

A BHA spokesman said that anyone riding work for a trainer, whether paid or not, is barred from placing lay bets against horses from that stable. As a bookmaker, Thompson might be thought to be in breach whenever he took bets on runners from those yards, but the case relates only to his personal betting transactions through an online exchange.

Moore said he had checked with the BHA before allowing a bookmaker to ride work on his horses and been advised that there was no objection. "He didn't ask us any questions about any of the horses," Moore said. "The particular horse that I believe he did lay, it wouldn't have wanted any figuring out – it was no good!"

No wrongdoing is alleged against either trainer. Thompson could not be reached for comment.

Sea Moon is "an intended runner" in next month's St Leger, according to a spokesman for his owner, Khalid Abdullah. Now the 6-4 favourite after a deeply impressive success in the Great Voltigeur last week, Sea Moon is one of 17 left in the race after Wednesday's forfeit stage.